Process and compositions for electroplating chromium



United States Patent US. Cl. 20451 28 Claims ABSTRACT OF THE DISCLOSURE A bright decorative plating process for electroplating chromium on a basis metal, characterized by high coverage and throwing power, utilizes a chromic acid plating bath containing the anion of a halogenated organic carboxylic acid having at least three carbon atoms. The baths are of high CrO to catalyst ratio, e.g. 125-55011. They may be of the self-regulating type. The halogenated carboxylic acid anion may be added by introducing into the bath the acid itself, or a soluble salt of the acid, or the acid anhydride. The anions of the halogenated aliphatic dicarboxylic acids such as 3,4-dichloroadipic acid and 2,2-dichlorosuccinicacid are preferred. The concentration of the halogenated carboxylic acid anion is preferably from to 100 grams per liter, but higher concentration up to saturation may be used.

This application is a continuation-in-part of application Ser. No. 421,600, filed Dec. 28, 1964, now abandoned.

This invention relates to a novel process and composition for electrodeposition of bright decorative chromium. More particularly, it relates to a chromium plating process characterized by highly satisfactory coverage of low current density areas.

As is well known to those skilled-in-the-art, chromium may be plated onto various basis metals. During chromium plating, it has been found that the coverage may not be completely satisfactory in low current density areas (typically below about 3-4 a.s.d.) and these areas may frequently receive little or no plate at all. Prior attempts to remedy this defect have included the use of auxiliary anodes; while this step may give some improvement, the disadvantages thereof are numerous and well known. Typically the burden of properly positioning the required anodes is undesirable and the cost of maintaining them on plating racks is very high.

Other techniques which have been tried include the use of various additives in the baths, but these additives have either been unable to give the desired result or have concurrently contributed some additional defect to the plate or to the process. Such defects may include the production of a blotching plate containing passivity spots, or result in an undesirably high degree of anode corrosion. Corrosion of lead anodes in chromium plating systerns is undesirable in that a massive sludge is formed on the bottom of the tank; and the lead anodes are eaten away and must be replaced at regular intervals. Because of these problems, it is well recognized that prior art attempts to attain high coverage over the entire surface of the cathode and particularly in the areas of low current density have not been completely successful.

It is an object of this invention to provide a process for electrodepositing bright decorative chromium plate, characterized by its high coverage of low current density areas. Other objects will be apparent to those skilled-inthe-art on inspection of the following description.

In accordance with certain of its aspects, the process of this invention, characterized by high coverage and by high throwing power, for electrodepositing a bright decorative chromium plate onto a basis metal may comprise maintaining an aqueous hexavalent chromium plating bath containing chromic acid and sulfate in ratio of -550: 1, and at least about 25 grams per liter of an anion of a halogenated organic carboxylic acid having at least three carbon atoms; and electrodepositing a chromium plate fbror; said bath onto said basis metal as cathode in said The chromium plating bath which may be employed in practice of this invention in an aqueous solution containing g./l.-500 g./l., typically 250 g./l.-400 g./l., say 250 g./l. of chromic acid CrO and 0.4 g./l.-3.3 g./l., say 1.2 g./l. of sulfate ion SO typically added as sodium sulfate. In practice of this invention, the ratio of CrO :SO may preferably be maintained at l25-550z1, typically ZOO-300:1, say 250:1.

It is a particular feature of this invention that the novel results may be attained (a) in a standard, non-self regulating bath as described supra or (b) in a mixed catalyst bath or (c) in a self-regulating bath. A typical mixed catalyst bath which may be employed may contain 150- 500 g./l., typically 250-400 g./l., say 250 g./l. of chromic acid CrO and 0.05-2.0 g./l., say 0.6 g./l. of sulfate 80.; ion; and 0.05-2.0 g./l., say 0.6 g./l. of silicofiuoride SiF ion. It will be noted that the ratio as the term is used in this application refers to the ratio wherein each of the quantities is expressed in grams. Other fluorides, including complex fluorides may be employed. When no other fluoride such as SiF is present, the ratio may become CF03 S04 In practice, the ratio of CrO to $0., plus SiF may preferably be maintained at l25-550z1, typically 200- 300:1, say 250:1. In the specification and claims, the ratio may, for convenience, be referred to as the ratio of chromic acid to sulfate; but it will be understood that the ratio as so designated may include as equivalent to sulfate, other inorganic ions including fluoride ions such as the silicofiuoride ion, the fluoborate ion, the fluotitanate ion, etc. Thus the designation chromic acid to sulfate includes chromic acid to sulfate plus other fluoride such as silicofiuoride if and when the latter is present.

This invention may also be used in a self-regulating bath, e.g. of the sulfate type, which may contain 150-500 g./l., typically 250-400 g./l., say 250 g./l. of chromic acid; and 0.6-10 g./ 1., say 5 g./l., of strontium sulfate; plus optionally an additionally strontium compound source of excess strontium ion, such as strontium hydroxide, strontium chromate, etc. in amounts to provide 0-12 g./l., say 4.5 g./l. of strontium ion, Sr++. The ratio of CrO to SO may preferably be maintained at 125-550z1, typically ZOO-300:1, say 250:1.

The halogenated organic carboxylic acids which may be added, either as such or e.g. as their anhydrides or salts (typically the sodium salt), to chromium plating baths in practice of this invention may typically include:

(a) monohalogenated aliphatic monocarboxylic acids having at least three carbon atoms,

(b) polyhalogenated aliphatic monocarboxylic acids having at least three carbon atoms,

(c) monohalogenated aliphatic polycarboxylic acids having at least three carbon atoms,

Typical illustrative monohalogenated aliphatic monocarboxylic acids having at least three carbon atoms which may be employed may include:

2-chloropropionic acid 3-brornopropionic acid 3-iodopropionic acid 2-ehlorobutanoic acid ehloropivalic acid (monochlorinated tertiary pentanoic acid) 2-chloropentanoic acid Typical illustrative polyhaalogenated aliphatic monocarboxylic acids having at least three carbon atoms Which may be employed may include:

2,2-dichloropropionic acid 2,2,3-trichloropropionic acid pentafiuoropropionic acid Typical illustrative monohalogenated aliphatic dicarboxylic acids having at least three carbon atoms which may be employed may include:

chloromalonic acid 2-chlorosuccinic acid Z-bromosuccinic acid 2-chloroadipic acid Typical illustrative polyhalogenated aliphatic dicarboxylic acids which may be employed may include:

2,2-dichlorosuccinic acid 2,2-dichloroadipic acid tetrachlorosuccinic acid 2,3-dibromosuccinic acid 3,3-diiodosuccinic acid 3,4-dichloroadipic acid Typical illustrative monohalogenated aromatic monoboxylic acids which may be employed may include:

3-chloro-4-sulfobenzoic acid 3-bromo-4-sulfobenzoic acid Typical illustrative monohalogenated aromatic dicarboxylic acids which may be employed may include:

4-chlorophthalic acid 2-bromoterephthalic acid Typical illustrative polyhalogenated aromatic monocarboxylic acids which may be employed may include:

3,5-dichloro-4-sulfobenzoic acid 3,6-dibrmo-4-sulfobenzoic acid Typical illustrative polyhalogenated aromatic dicarboxylic acids which may be employed may include:

3,4-dichlorophthalic acid 3,4-dibromophthalic acid 4,5-dichlorophthalic acid Other acids falling within the scope of this invention will be apparent to those skilled-in-the-art.

The preferred acids include halogenated aliphatic dicarboxylic acids having at least three carbon atoms and most preferably a halosuccinic acid such as 2-chlorosuccinic acid or 2,2-dichlorosuccinic acid or a haloadipic acid such as 3,4-dichloroadipic acid.

In practice of this invention, the carboxylic acid is added to the electroplating bath in amounts from 25 g./l.

up to the maximum practical concentration such as saturation, and preferably from 25 to 100 g./l. For many purposes the concentration may be in the narrower range from 25 to 50 g./l. The acids employed will preferably be those having a solubility in the plating bath within these ranges. Solubilizing substituents such as sulfo groups may be included in the carboxylic acid in order to increase solubility in the plating bath.

A typical composition which may be premixed, and added to a water solution in which the concentration of SO ion and components including, e.g., SiF may be adjusted separately, may includes the compositions indicated in Tables I and 11 below (here as elsewhere, unless otherwise indiacted, all parts are parts by weight). It Will be apparent that these compositions, like other chromic acid containing compositions, should preferably be formed, maintained, and stored in a manner to minimize contact with extraneous organic compositions and materials; and preferably they will be formed, stored, and maintained at temperature below C. It Will also be apparent that in compositions hereinafter designated as containing halo-organic acid, halo-organic acid containing at least three carbon atoms is intended and equivalent amounts of anhydride, salt, etc. may be employed, thus yielding appropriate amounts of the desired ion.

TABLE I Max- Min- Componenl; imum imum Preferred A Preferred B CrO 500 150 250 400 Halocrganic acid 25 30 40 A preferred composition may include:

TAB LE II Max- Min- Gomponent imum imum Preferred A Preferred B CrOa 500 250 400 2,2-dic-hloro succinic acid- 100 25 30 40 The halo-organic acid may be added as such, as the anhydride, or as the salt, typically as the sodium salt. In the preferred embodiment, the additive may be admixed with the other ingredients to be used to make up the bath. Typically such a composition may include:

1 Typically supplied as, e.g., sodium sulfate.

A specific self-regulating composition may include:

TABLE IV Max- Min- Component imum imum Preferred A Preferred B 500 150 250 400 10 4 4 8 28 0 4. 5 0 2,2diehlorosuccinic acid. 100 25 3O 40 A typical mixed catalyst composition may include:

TABLE V Max- Min- Component imum imum Preferred A Preferred B 500 150 250 400 2.0 0.05 0.5 1.3 2. O O. 05 0. 5 0. 7 Halo-organic acid 100 25 3O 40 1 Typically added as sodium sulfate. 2 Typically added as sodium silica fluoride.

A typical self-regulating composition having both sulfate and silicofiuoride may include:

TABLE VII Max- Min- Component imum imum Preferred A Preferred B 500 150 250 400 2. O. U. 5 1. 3 2. 0 0. 05 0. 5 0. 7 9 O. 2 5. 0 2. 6 27 6. 0 15 27 Halo organic acid 100 25 30 40 A preferred self-regulating composition may include:

TABLE VIII Max- Min- Component imum imum Preferred A Preferred B ClOs 500 150 200 325 SrSOr 8 0. 1 2. 0 4. 0 K- SiFa 6 0.75 2.0 3.5 Sr 0104. l5 0 9 6 K- Cr:O7 100 25 75 100 2,2-dichlorosuceinic acid. 100 25 30 40 The baths useful in practice of this invention may be formed by dissolving the above compositions in aqueous medium to form baths containing e.g. 150-500 g./l. of CrO and corresponding quantities of the other components.

It is found that particularly outstanding results, in terms of handleability, packaging, ease of manufacture, as well as maximum coverage and brilliance of chromium deposit accompanied by a minimum of lead anode corrosion may be obtained when in the compositions of Tables I, III, V, and VII, the halo-organic acid is an aliphatic dicarboxylic acid having at least three carbon atoms; and such compositions are most highly preferred, because of their peculiarly unexpected superiority.

The baths of this invention which may be employed to readily and conveniently electrodeposit chromium plate, are characterized by high coverage and by high throwing power. These baths may be used to deposit chromium onto any basis metal. It is a particular feature of this invention that outstanding results may be obtained when the basis metal is a metal having an atomic number of 24-30. Typical of such basis metals are chromium, manganese, iron, cobalt, nickel, copper, and Zinc. Mixtures or alloys of these metals may be platedtypically brass, stainless steel, etc. The preferred basis metal may be nickel, and preferably active nickel.

The preferred active nickel basis metal may be attained by electrodeposition of nickel onto a suitable substrate metal (such as iron).

Active nickel may be nickel which is highly receptive to the deposition thereon of a bright clear decorative plate and which has a surface which may be free of nickel compounds such as the oxide. Typically nickel may be active when freshly plated onto a cathode. If not already active, the nickel may be rendered active by cathodic or other reducing treatment prior to the deposition of chromium plate thereon. Preferably this may be effected by maintaining the nickel as cathode in an aqueous elec trolyte solution, preferably containing an acid. The preferred acids for use in either electrolytic or non-electrolytic techniques may include acids such as the common mineral acids e.g. hydrochloric acid or sulfuric acid, etc. When the aqueous electrolyte solution is other than acid, it may preferably be followed by an acid dip.

It has been found when the high ratio baths of this invention are used to plate chromium onto bright nickel basis metal that it is advantageous to activate the bright nickel by applying to the cathode to be plated in the bath, a low voltage applied thereto at a time less than about five seconds after immersion and preferably to apply the voltage prior to immersion of the cathode. The low voltage may be sufficient to produce a cathode current density up to about 0.250.5 times the plating current density. Then the current density may be raised to its full operating value. This technique makes a bright nickel surface more receptive to the deposit of bright chromium from the baths of this invention.

The bath may be preferably at temperature of 3060 C., say 3550 C. A preferred cathode current density may be 0.340 amperes per square decimeter (a.s.d.) most preferably 0.5-20 a.s.d. Plating may be carried out with air or mechanical agitation for any time to obtain a desired thickness, but for decorative plate it is usually 1-10 minutes; and typically about five minutes may suffice.

During plating in accordance with the process of this invention, there is unexpectedly and surprisingly no appreciable loss of the halo-organic acid by decomposition over extended periods of time. For example, in tests, 2,2- dichlorosuccinic acid was found still to function satisfactorily after plating had been carried out for 110 ampere hours per liter and even longer.

At the conclusion of the plating time, the cathode Will be found to be covered to a remarkable degree with clear, bright, decorative chromium plate. It is a particular feature of this invention that the plate is unexpectedly characterized by its high coverage Without the need for conforming anodes. For example, articles containing deep recesses such as zinc based die cast automotive dashboard trim may be plated by the process of this invention (with no conforming anode) to unexpectedly yield a bright, uniform plate on both high and low current density areas. This has not heretofore been possible.

The plate produced by the novel process of this invention may be found to be highly satisfactory with respect to its unusually bright, decorative appearance and its resistance to corrosion.

In the following series of illustrative examples, chromium was electrodeposited onto a 100 mm. nickel-plated brass panel in a standard Hull Cell at 49 C. for five minutes and three amperes. A standard stock bath containing 300 g./l. chromic acid and 1.3 g./l. of sulfate (added as sulfuric acid) was employed. The halo-organic acid was added in the amount (in g./l.) indicated. At the end of the test, the Hull Cell panel was inspected and the distance across the panel bearing a plate of clear bright chromium was measured in millimeters.

TABLE IX G./l. Coverage, Acid added mm.

Example:

1 None 57 2 2,2 dichlorosucciuie acid 25 77 3 .do 29 77 4 .do 33 79 5 Tetrachlorosuceinic aeid 25 6 2,3-dibromosuccinic acid 25 70 7 3,4-dichlotoadipic acid 25 79 8 2-chloropr0pionie acid 25 73 9 o 32 77 10 d0 45 76 11 3-ehloropropionic acid 25 76 12 2,2-diehloropropionic acid 36 73 13 2,2,3trichloropropionic acid 30 78 14 3-brom0propi0nie acid 25 77 In the following series of illustrative examples the stock bath and the plating conditions were the same as in the previous examples, except that electrodeposition was conducted at 43 C.

In the following series of examples, chromium was electrodeposited onto Hull Cell panels at 43 C. for five minutes and three amperes from a series of mixed catalyst baths containing 400 g./l. of chromic acid and sulfate, silicofiuoride and halo-organic acid in the amounts (in g./l.) indicated.

Thus it will be seen that the loss in Weight of the lead is much lower .(only 4.4% as much) when the baths of this invention are used than when a bath is used containing trichloroacetic acid.

It had been believed that the organic compounds used in practice of this invention would be quickly oxidized in the presence of chromic acid, a well known oxidizing agent and thus be substantially inoperable. It is however a particular feature of the baths of this invention containing halo-organic acids such as 2,2-dichlorosuccinic acid, that they may unexpectedly be stable over extended periods of operation.

In the following series of examples, chromium was electrodeposited onto Hull Cell panels at 43 C. for five minutes and three amperes from a series of self-regulating baths containing 425 g./l. of chromic acid, 8.0 g./l. of strontium sulfate. The halo-organic acid was added in the amount (in g./l.) indicated.

From :Examples 1, 15, 17, and 23, it may be observed that with no halo-organic acid added, the panel was respectively covered for a distance of 57 mm., 58 mm., 55 mm, and 52 mm. and these may be considered control examples for the examples which follow. As the 2,2-dichlorosuccinic acid concentration increased, e.g. from g./l. to 33 g./l., the coverage increased to as high as 79 mm. A dilference of 23 mm. or more may be considered significant. Example 4 was carried out in a bath which had been functioning for 40 ampere hours per liter, this indicating that the system including 2,2-dichlorosuccinic acid was stable over an extended period. Similarly Example 8 was carried out after a life test for 65 ampere hours per liter. Thus, it will be apparent from these examples, that practice of this invention permits attainment of a high degree of coverage.

It is also a feature of the baths of this invention that the preferred halo-organic carboxylic acids herein disclosed are characterized by their substantially decreased degree of attack of lead anodes. This latter may be observed for example by immersing lead in two baths containing 350 g./l. CrO and 1.4 g./l. SO.,=. The baths, together with the indicated additive, may be left to stand for 22 hours at 49 C., then electrolyzed at 15 a.s.d. for one hour and then left to stand again for 65 hours at approximately 21 C. with the following results:

In order to demonstrate the stability of the baths of this invention under severe operating conditions, a bath may be prepared containing 300 .g./l. CrO 1.3 g./l. SO and g./l. of 2,2-dichlorosuccinic acid. The bath may be heated to 93 C. and electrolyzed at a high current density of 60 a.s.d. (94 amperes per liter of solution). Electrolysis may continue over four hours at 93 C. using a lead anode and a steel cathode. At the conclusion of the test, the voltage drop across the bath may be noted and found to be unchanged. This indicates that no trivalent or reduced chromium is present and thus that no 2,2-dichlorosuccinic acid had been oxidized. As is well known to those skilled-in-the-art, acids such as citric acid, tartaric acid, oxalic acid, etc. (which are not within the scope of this invention) would oxidize substantially immediately on contact with chromium baths.

Although the outstandingly high coverage herein noted maybe attained by the several halo-acids set forth, it may be found that halogenated dicarbox-ylic aliphatic acids having at least three carbon atoms are unexpectedly superior in that they permit operation at desirably high ratio (of e.g. CrO to $05) with high coverage and minimum attack on anodes. For example, such acids typified by 3,4-dichloroadipic acids, may give maximum coverage, with a lead anode corrosion which is unexpectedly and significantly less than that attained when acids such as trichloroacetic acid are used. Furthermore, loss of acid such as halogenated adipic acids from plating baths may be found to be considerably less from evaporation than loss of e.g. halogenated acetic acid from these baths. These factors, inter alia, dictate that the acids having at least three carbon atoms permit attainment of unexpectedly superior advantages.

It is a particularly outstanding feature of the preferred embodiment of this invention that when halogenated dicarboxylic acids such as halogenated succinic acid and halogenated adipic acid are used that the coverage with chromium plate is extremely high, and interior portions of the cathodes are uniformly covered by a bright, decorative plate. Furthermore, the color, brilliance, and clarity of the plate on the open or exposed areas is far superior to that attained by use of the best prior art baths. The process is further characterized by freedom from anode attack and by substantially lower tendency toward undesirable development of chromate-film on low current density areas which would decrease the appearance and fications thereof which clearly fall within the scope of the invention will be apparent to those skilled-in-the-art.

We claim:

1. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorative chromium plate onto a basis metal which comprises maintaining an aqueous hexavalent chromium plating bath containing chromic acid and sulfate in ratio of 125-55021 and at least about 25 grams per liter of an anion of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboXylic acids having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

2. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorative chromium plate onto a basis metal which comprises maintaining an aqueous hexavalent chromium plating bath containing chromic acid and sulfate in ratio of l25-550:l and at least about 25 grams per liter of an anion of a halogenated aliphatic dicarboxylic acid having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

3. The process as claimed in claim 2 for electrodepositing a bright decorative chromium plate onto a basis metal wherein said acid is a chlorinated adipic acid.

4. The process as claimed in claim 2 for electrodepositing a bright decorative chromium plate onto a basis metal wherein said acid is a chlorinated succinic acid.

5. The process as claimed in claim 2 for electrodepositing a bright decorative chromium plate onto a basis metal wherein said halogenated organic acid is present in said bath in amount of 25 to 100 grams per liter.

6. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorative chromium plate onto a basis metal which comprises maintaining an aqueous chromium plating bath containing 150-500 g./l. chromic acid and 0.4-3.3 g./l. sulfate ion, and a ratio of chromic acid to sulfate of 125- 550:1, and from 25 to 100 g./l. of an anion of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

7. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorative chromium plate onto a basis metal which comprises maintaining an aqueous mixed-catalyst chromium plating bath containing 150-500 g./l. of chromic acid, 0.05-2.0 g./l. of sulfate ion and 0.05-2.0 of silicofluoride ion, the ratio of chromic acid to sulfate ion plus silicofluoride ion being 125-55021, and 25-100 g./l. of an anion of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

8. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorataive chromium plate onto a basis metal which comprises maintaining an aqueous self-regulating chromium plating bath containing 150-500 g./l. of chromic acid, 0.6- g./l. of strontium sulfate and 0-12 g./l. of excess strontium ion, the ratio of chromic acid to sulfate being 125-55021 and 25-100 g./l. of an anion of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

9. A composition for addition to an aqueous medium to form a bath for the electrodeposition of bright Component Maximum Minimum C hromic acid 500 150 Sulfate ion 3. 3 0. 4 Halo-organic acid- 25 the ratio of chromic acid to sulfate being 550:1 and the halo-organic acid being a halogenated organic acid selected from the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least three carbon atoms.

10. A composition as claimed in claim 9 for addition to an aqueous medium to form a bath for the electro deposition of bright chromium plate onto a basis metal wherein said halo-organic acid is 3,4-dichloroadipic acid.

11. A composition as claimed in claim 9 for addition to an aqueous medium to form a bath for the electrodeposition of bright chromium plate onto a basis metal wherein said halo-organic acid is 2,2-dichlorosuccinic acid.

12. A composition for addition to an aqueous medium to form a bath for the electrodeposition of bright chromium plate onto a basis metal consisting essentially of the following componetns in the designated parts by weight:

Component Maximum Minimum 500 2. 0 0. O5 2. 0 0. 05 Halo-organic acid 100 25 Component Maximum Minimum Halo-organic acid 100 25 the ratio of chromic acid to sulfate plus silicofluoride being 125-550:1 and the halo-organic acid being a halogenated organic acid selected from the group consisting of aliphtaic and aromatic monocarboxylic and dicarboX- ylic acids having at least three carbon atoms.

14. A chromium plating solution for the electrodeposition of bright chromium plate onto a basis metal which comprises an aqueous solution of chromic acid and sulfate in ratio of 125-550z1, and at least 25 grams per liter of an anion of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least 3 carbon atoms.

15. A chromium plating solution as claimed in claim 14 for the electrodeposition of bright chromium plate onto a basis metal wherein said halogenated organic carboxylic acid is 2,2-dichlorosuccinic acid.

16. A chromium plating solution as claimed in claim 14 for the electrodeposition of bright chromium plate onto a basis metal wherein said halogenated organic acid is present in amount of 25 to 100 g./l.

17. A chromium plating solution for the electrodeposition of bright chromium plate onto a basis metal which comprises an aqueous solution of 150-500 g./l. of chromic acid, 0.05-2.0 g./1. of sulfate ion and 0:05-20 g./l. of silicofluoride ion, the ratio of chromic acid to sulfate 1 1 plus silicofluoride being 125-550z1, and 25-100 g./l. of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least 3 carbon atoms.

18. A chromium plating solution for the electrodeposition of bright chromium plate onto a basis metal which comprises an aqueous solution of 150-500 g./l. of chromic acid, 0.6-10 g./l. of strontium sulfate, the ratio of chromic acid to sulfate being l25-550:l, and -12 g./l. of excess strontium ion, and 25-100 g./l. of an anion of a halogenated organic acid of the group consisting of aliphatic and aromatic monocarboxylic and dicarboxylic acids having at least 3 carbon atoms.

19. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorative chromium plate onto a basis metal which comprises maintaining an aqueous chromium plating bath containing 150-500 g./l. chromic acid and 0.4-3.3 g./l. sulfate ion, and a ratio of chromic acid to sulfate of 125- 550z1, and from 25 to 100 g./l. of an anion of a halogenated aliphatic dicarboxylic acid having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

20. The process characterized by high coverage and by high throwing power for electrodepositing a bright decorative chromium plate into a basis metal "which comprises maintaining an aqueous mixed-catalyst chromium plating bath containing 150-500 g./l. of chromic acid, 0.05-2.0 g./l. of sulfate ion and ODS-2.0 g./l. of silicofluoride ion, the ratio of chromic acid to sulfate ion plus silicofluoride ion being 125-55011, and 25-100 g./l. of an anion of a halogenated organic dicarboxylic acid having at least three carbon atoms, and electrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

21. The process characterized by high coverage and by high throwing power for electrode-positing a bright decorative chromium plate onto a basis metal which comprises maintaining an aqueous self-regulating chromium plating bath containing 150-500 g./l. of chromic acid, 0.6- g./l. of strontium sulfate and 0-12 g./l. of excess strontium ion, the ratio of chromic acid to sulfate of 125-550z1 and 25-100 g./l. of an anion of a halogenated aliphatic dicarboxylic acid having at least three carbon atoms; and elcctrodepositing a bright decorative chromium plate from said bath onto said basis metal as cathode in said bath.

22. A composition for addition to an aqueous medium to form a bath for the electrodeposition of bright chromium plate onto a basis metal consisting essentially of the following components in the designated parts by weight:

Component Maximum Minimum Chromio acid 500 150 Sulfate ion 3 3 0.1%

Halo-organic aci the following components in the designated parts by weight:

Component Maximum Minimum Chromic acid 500 150 Sulfate ion 2. 0 0. 05 Silicofluoride ion 2. 0 0. O5 Halo-organic acid 25 Component Maximum Minimum Halo-organic acid 100 25 the ratio of chromic acid to sulfate plus silicofiuoride being -550:1 and the halo-organic acid being a halogenated aliphatic dicarboxylic acid having at least three carbon atoms.

25. A chromium pltaing solution for the electrodeposition of bright chromium plate onto a basis metal which comprises an aqueous solution of chromic acid and sulfate in ratio of 125-550z1, and at least 25 grams per liter of an anion of 3,4-dichloroadipic acid.

26. A chromium plating solution for the electrodep osition of bright chromium plate onto a basis metal which comprises an aqueous solution of chromic acid and sulfate in ratio of 125-55021, and at least 25 grams per liter of anion of 2,2'-dichlorosuccinic acid.

27. A chromium plating solution for the electrodep- 'osition of bright chromium plate onto a basis metal which comprises an aqueous solution of -500 g./l. of chromic acid, 0.0=5-2.0 g./l. of sulfate ion and 0.05-2.0 g./l. of silicofiuoride ion, the ratio of chromic acid to sulfate plus silicofluoride being 125-550zl, and 25-100 g./l. of a halogenated aliphatic dicarboxylic acid having at least 3 carbon atoms.

28. A chromium plating solution for the electrodeposition of bright chromium plate onto a basis metal which comprises 150-500 g./l. of chromic acid, 0.6-10 g./l. of strontium sulfate, the ratio of chromic acid to sulfate being 125-550z1, and 0-12 g./l. of excess strontium ion, and 25-100 g./l. of an anion of a halogenated aliphatic dicarboxylic acid having at least 3 carbon atoms.

References Cited UNITED STATES PATENTS 2,623,847 12/ 1952 Gilbert et al. 2045l 2,640,022. 5/ 3 Stareck 204-51 3,248,310 4/1966 Schaer 204-51 3,282,812 11/1966 Brown et al. 2045l JOHN H. MACK, Primary Examiner G. L. KAPLAN, Assistant Examiner 

